Phenolic-resin binders have conventionally been in widespread used as binders for joining together the fibers in heat-insulating sound-absorbing members composed of glass wool, rock wool, or other inorganic fibers. Phenolic-resin binders are heat-cured in a relatively short period of time, and a strong binder cured product is obtained. Inorganic-fiber heat-insulating sound-absorbing members in which phenolic-resin binders are used are therefore exceptional in regard to their shape retention, thickness recovery after unpacking from a compressed state, deformation resistance, and other properties. However, when phenolic-resin binders are used, formaldehyde is released during the production process, particularly while curing the binder, and readily remains in the product. Recently, concerns related to reducing environmental load have prompted restrictions to be placed by laws and regulations on the amount of formaldehyde emitted by products. Efforts are therefore underway to produce inorganic-fiber heat-insulating sound-absorbing members using formaldehyde-free binders.
Acrylic-resin binders are a type of formaldehyde-free binder. However, under weakly acidic to weakly basic conditions, acrylic-resin binders do not readily cure, and strong binder cured products are not readily obtained. When the binder is used, the pH thereof has accordingly been adjusted to approximately 3, and curing is promoted.
However, strongly acidic binders readily corrode piping for supplying the binder, spraying devices, mesh conveyors for depositing inorganic fibers, and other production equipment; and problems have been presented in regard to rising equipment maintenance expense, equipment cost, and other expenditures. Highly acidic effluents are also discharged, and the costs of treating these effluents have also presented problems.
Aqueous binders containing an acrylic resin and a cross-linking agent containing one or more types of alkanolamine are disclosed in Patent Documents 1 and 2 below as acrylic-resin binders that are appropriate for use under weakly acidic to weakly basic conditions. In Patent Documents 1 and 2, inorganic-acid ammonium salts may also be included at 0.1 to 5 parts by mass relative to a sum of 100 parts by mass of the acrylic resin and the cross-linking agent, with the object of neutralizing the alkaline components dissolved out from the inorganic fiber and minimizing hydrolysis of the binder cured product.